Influence of corona on the voltages induced by nearby lightning on overhead distribution lines

A model for the calculation of lightning-induced voltages is presented with the aim of assessing the effect of corona when power distribution lines ar e illuminated by lightning electromagnetic fields, Corona is taken into acc ount by means of dynamic capacitance describing a charge-voltage diagram, S uch an equivalent capacitance is then introduced in a model which describes a line illuminated by a lightning electromagnetic field, It is first concl uded that the influence of corona on lightning induced overvoltages is of i mportance only for particularly severe strokes. It is also found that coron a acts to increase the magnitude of these overvoltages, contrary to the cas e of voltages due to direct strokes, which are attenuated by corona, A theo retical explanation of such an amplitude increase is presented, The effect of the ground resistivity is also taken into account in the calculations. T he results show that such an effect is in general as important as the effec t of corona, This is different from the direct-strike behavior, where coron a, when present, affects the surge propagation more than the ground resisti vity. This is due to the fact that for the case of induced-voltages, the gr ound resistivity may affect more strongly the lightning-radiated fields rat her than the surge propagation along the line, while corona affects only su rge propagation. The need for experimental results to test the theoretical finding of the paper is stressed and some indication is given. Finally, a s ensitivity analysis of the induced voltages as a function of the charge-vol tage diagram adopted to model corona is also performed.